McIntosh MC 2250 User manual

THEMclNTOSHMC2250SOLIDSTATESTEREOPOWERAMPLIFIER
ReadingTime:31Minutes Price$2.00

VARIOUSREGULATORYAGENCIESREQUIRETHATWEBRINGTHEFOLLOWING
INFORMATIONTOYOURATTENTION.PLEASEREADITCAREFULLY.
WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNITTO
RAINORMOISTURE.
TheMclntoshyouhavepurchasedisa Model
MC2250.Ithasa serialnumberlocatedontherearpanel
ofthechassis.Recordthatserialnumberhere:
Themodel,serialnumberandpurchasedateareim-
portanttoyouforanyfutureservice.Recordthepur-
chasedatehere:
Uponapplication,MclntoshLaboratoryprovidesa
Three-YearServiceContract.YourMclntoshAuthorized
ServiceAgencycanexpediterepairswhenyouprovide
theServiceContractwiththeinstrumentforrepair.To
assist,recordyourServiceContractnumberhere:
SerialNumber
Purchasedate
ServiceContractNumber

YourMC2250StereoPowerAmplifieris
designedtoperformtoitsspecificationsfor
manyyears.Ifyouhaveanyquestions,please
contact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903-9990
Phone:[phone]
MclNTOSHTHREEYEARSERVICECONTRACT
AnapplicationforA THREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:
1.Mclntoshwillprovideallparts,materials
andlaborneededtoreturnthemeasured
performanceoftheinstrumenttothe
originalperformancelimits.TheSER-
VICECONTRACTdoesnotcoverany
shippingcoststoandfromtheauthoriz-
edserviceagencyorthefactory.
2.AnyMclntoshauthorizedserviceagency
willrepairMclntoshinstrumentsatnor-
malservicerates.Toreceiveservice
underthetermsoftheSERVICECON-
TRACT,theSERVICECONTRACTCER-
TIFICATEmustbepresentedwhenthe
instrumentistakentotheserviceagency.
3.Alwayshaveservicedonebya
Mclntoshauthorizedserviceagency.If
theinstrumentismodifiedordamaged
asa resultofunauthorizedrepair,the
SERVICECONTRACTwillbecancelled.
Damagebyimproperuseormishandl-
ingisnotcoveredbytheSERVICE
CONTRACT.
4.TheSERVICECONTRACTisissuedto
youastheoriginalpurchaser.Topro-
tectyoufrommisrepresentation,this
contractcannotbetransferredtoa se-
condowner.
5.ToreceivetheSERVICECONTRACT,
yourpurchasemustbemadefroma
Mclntoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfor
theSERVICECONTRACTmustbepost-
markedwithin30daysofthedateof
purchaseoftheinstrument.
7.ToreceivetheSERVICECONTRACT,all
informationontheapplicationmustbe
filledin.TheSERVICECONTRACTwill
beissuedwhenthecompletelyfilledin
applicationisreceivedbyMclntosh
LaboratoryIncorporatedinBinghamton,
NewYork.
8.UnitsinoperationoutsidetheUnited
StatesandCanadaarenotcoveredby
theMclntoshSERVICECONTRACT,ir-
respectiveoftheplaceofpurchase.Nor
areunitsacquiredoutsidetheU.S.A.
andCanada,thepurchasersofwhich
shouldconsultwiththeirdealertoas-
certainwhat,ifany,servicecontractor
warrantymaybeavailablelocally.
Copyright1982© byMclntoshLaboratoryInc.
-1-
Contents
SERVICE1
INSTALLATION2
HOWTOCONNECT4
FRONTPANELCONTROLS
ANDHOWTOUSETHEM9
REARPANELINFORMATION11
PERFORMANCELIMITS12
PERFORMANCECHARTS13
TECHNICALDESCRIPTION15
BLOCKDIAGRAM17
TakeAdvantageof3 years
ofContractService...
FillintheApplicationNOW.

Removethethreescrewssecuringtheshipping
palletandremovethepalletandbottomshipping
pad.Removetheplasticshippingbag.Ifthe
amplifieristobemountedina cabinetorrack
mount,removethefourplasticfeetfromthebottom
oftheamplifier.Iftheamplifierisusedalone,leave
thefeetscrewedtotheamplifier.Theyare
necessarytoholdtheamplifierabovethesupporting
surfacetoallowadequateventilation.Theamplifier
can notbeusedwithoutventilationthroughthe
chassisandheatsinks.
INSTALLATIONINA MclNTOSHCABINET
Installtheamplifierbyfollowingtheinstructions
enclosedwiththecabinet.
TheMC2250canbehousedina MclntoshL54
cabinet,installedina customcabinetormountedin
astandard19inchrackbyusingtheadditionof
RACKMOUNTINGADAPTERS(RMA7).TheMC2250
weights80pounds(36.3kg).Inanyinstallationitis
necessarytoprovidepropersupportfortheweight.
Themountingmethodsdescribedandtheamplifier
havebeendesignedtoaccomodatetheweight.Be
surethatthepanelinwhichtheamplifierismounted
canalsohandletheweight.
UNPACKINGTHEAMPLIFIER
Removetheamplifierandhardwarepackagefrom
theouterandinnershippingcartons.Becarefulto
avoidmaringorplacinga strainontheedgesofthe
frontpanel.Placetheamplifierupsidedownona
surfacethatwillsupportthetransformerandheat-
sinksbutwillnottouchtheedgeofthefrontpanel.A
padfromtheshippingcartoncanbeusedforthis
purpose.
INSTALLATIONINA CUSTOMCABINET
Thetrouble-freelifeofanelectronicinstrumentis
greatlyextendedbyprovidingsufficientventilation
aroundit.Thispreventsthebuildupofhighinternal
temperaturesthatcausedeterioration.Allow
enoughclearancesothatcoolaircanenteratthe
bottomofthecabinetandbeventedfromthetop.
Withadequateventilationtheinstrumentcanbe
mountedinanyposition.Therecommended
minimumspaceforinstallationis15inches(38.1
cm)deep,17inches(43.2cm)wide,and8 inches
(20.3cm)high.
Verticalmountingoftheamplifierrequirescareful
consideration.Thetotalweightissupportedbythe
panelandshelfonwhichtheamplifieristobe
mounted.Thoughtshouldbegiventoprovidinga
meansforraisingtheamplifieroutofthepanel.
Moreconsiderationshouldbegiventoproviding
adequateventilationatthepanelinverticalmoun-
ting.Theheatsinksareattherearofthechassisper-
mittingtheheattopassovertheentirechassis.Itis
thentrappedbehindthepanelcausingtheoverall
temperaturetorise.Inanycase,airflowforcooling
canbeimprovedbytheuseofa properlyinstalled
lownoisefan.Adequatecoolingwillextendthelife
oftheamplifier.
DEPTHREQUIRED
TOPOFSHELF& BOTTOM
OFCUTOUTSHOULDCOINCIDE.
Fig.1.Viewsshowingmountingshelfinposition.
-2-
MOUNTINGSCREWS
DIFFERENCEBETWEENSCREW
LENGTH& TOTALSHELFTHICKNESS
MUSTNOTEXCEED1/2"
SHELF

1/4"DIA.(2HOLES)
Fig.2.Topviewofthepanelcutoutandmountingshelf.
INSTALLATIONPROCEDURE
1.MarkforPosition
Markthecabinetpanelwheretheinstrumentis
tobeinstalled.ThesolidlinesinFig.1 represent
theoutlineoftherectangularcutouttobemade
andalsorepresenttheoutsidedimensionsofthe
chassis.Makesuretoclearinternalshelves,parti-
tions,oranyequipment.Thebrokenlinerepre-
sentstheoutsidedimensionofthepanel.
2.DrillHoles
Usinga drillbitslightlylargerthanthetipof
yoursawblade,drilloneholeateachoftwodia-
gonallyoppositecorners.Theholesshouldbarely
touchtheinsideedgeoftheoutline.
3.SawPanelCutout
Placethebladeofthesawinoneoftheholes.
Sawingcarefullyontheinsideofthelines,first
makethetwolongcutsandthenthetwoshort
cuts.Aftertherectangularopeninghasbeencut
out,usea filetosquarethecornersandsmooth
anyirregularitiesinthecutedges.
4.ShelfInstallation
Inthesamewaymarkandsawtheventilation
cutoutshowninFig.2.Alsodrilltwo¼"holesfor
themountingscrews.Installtheshelftothe
cabinetpanel.Itmustbeabletosupportthetotal
weightoftheinstrument.
5.InstallInstrument
GuidetheACpowercordthroughthepanel
openingtothebackofthecabinet;then,slidethe
instrumentintotheopeninguntilitsfrontpanelis
flushwiththecabinetpanel.Securetheamplifier
totheshelfwith#10woodscrewsoftheproper
length.
½"thickshelf—use1"screws
¾"thickshelf—use1¼" screws
Donotuselongerscrews.Theymaypenetrate
electroniccomponentsinsidethechassisand
causeseveredamage.Thescrewlengthmustnot
exceedtheshelfthicknessbymorethan½".
INSTALLATIONINA 19INCHRACK
TheoptionalRMA7RACKMOUNTINGADAPTERS
installoneachendoftheamplifierfrontpanel.On
eachsideoftheamplifier,threescrewssecurethe
frontpanelbrackettothechassis.SeeFig.3.
Removethesethreescrews,placetheRACKMOUN-
TINGADAPTERoverthescrewholes,andreplace
thescrews.Theentireamplifierweightistransmit-
tedthroughtheRACKMOUNTINGADAPTERStothe
rack.Additionalsupportfortheamplifiercanbepro-
videdattherearofthechassisasdesired.
Fig.3.RackMountingAdaptersinstalled.
-3-
VENTILATION
CUTOUT
PANEL
CUTOUT
FRONTPANEL
MTG.SURFACE

HowtoConnect
INPUTCONNECTIONS
STEREOOPERATION
Useshieldedcablestoconnectthesignalfrom
thepreamplifierorsignalsourcetothepower
amplifier.Tominimizethepossibiltyofhumthe
shieldedcablesshouldberunparalleltoeachother
orlooselytwistedtogether.Locatethecablesaway
fromspeakerleadsandACpowercords.Allconnec-
tionsaremadeonthebackpaneloftheMC2250.
Forstereooperation,theleftoutputofthe
preamplifiershouldbepluggedintotheLeftINPUT
jackofthepoweramplifier.Therightoutputofthe
preamplifiershouldbepluggedintothe
Right/MONOINPUTjackofthepoweramplifier.
InstereooperationtheMODESWITCHmustbein
theSTEREOposition.
MONOPHONICOPERATION
FormonophonicoperationtheMODEswitchon
thebackpaneloftheMC2250mustbeplacedinone
oftheMONOpositions.Fortheproperchoice,see
thesectiononmonophonicoutputconnections.
Connecta shieldedcablefromthesignalsourceto
theRight/MONOINPUTjackoftheMC2250.The
LeftINPUTisnotused.
BecertainthattheMC2250isneveroperatedin
thestereomodewiththeoutputsconnectedfor
monophonicoperation.ShouldtheMODESWITCH
beleftintheSTEREOpositionandtheoutputsre-
mainstrappedfora monoparallelload,one
amplifierchannelwillattempttodrivetheother
whichcauseshighcirculatingcurrentsand
overheating.
OUTPUTCONNECTIONS
BecertaintheloudspeakersconnectedtotheMC
2250arecapableofhandlingthepoweroutputofthe
amplifier.
Selectionofthepropergaugewiretoconnectthe
loudspeakerstotheamplifierpreservesthequality
ofsoundreproductionforwhichtheloudspeakers
havebeendesigned.Ifundersizewireisused,
resistanceisaddedtotheamplifier/loudspeaker
combinationwhichadverselyaffectstheperfor-
mance.Addedresistancecausesdepreciationof
dampingcharacteristics,modificationoffrequency
responseandreductioninpowertotheloudspeaker.
Uselampcordorwirewithsimilarinsulationto
connectthespeakerstotheamplifier.Inallcases,
theleadstoandfromthespeakershouldbetwin
parallelconductorortwistedpair.Whenusing8
ohmspeakersandforthenormallyshortdistances
ofunder30feetbetweentheamplifierandspeaker,
#18wireorlargercanbeused.Fordistancesover30
feeta largerdiameterwireisrequired.Selectthe
correctsizefromthechartbelow.TheDCresistance
ofthespeakerleadsshouldbelessthan5%ofthe
speakerimpedance.Resistanceoftheleadsmust
becomputedforthelengthofwirebothtoandfrom
thespeakerorspeakers.
MAXIMUMWIRELENGTHS
Wire
Gauge
18
16
14
12
10
For4 OhmLoad
Feet
15
25
40
60
100
Meters
4.57
7.62
12.19
18.29
30.48
For8 OhmLoad
Feet
30
50
80
120
200
Meters
9.14
15.24
24.38
36.58
60.96
Wirelengthsaboverepresentthewireresistance
equalto5%ofthespeakerimpedance.
Formultiplespeakeroperation,runseparate
leadsfromtheamplifiertothespeakers.
STEREOOPERATION
Firstchecktheimpedanceofthespeakertobe
connected.Thisisusuallyfoundonthespeaker
systemneartheterminalsorinthespeakerlitera-
ture.TheproperterminalsontheMC2250canthen
beused.Connectthe+ orratedimpedanceter-
minaloftheleftspeakertothecorrespondingLEFT
OUTPUTterminalontheamplifier.Connectthe- or
thecommonterminaloftheleftspeakertotheleft
COMMONoutputterminaloftheamplifier.Inthe
samewayconnecttherightspeakertotheamplifier
RIGHTOUTPUTterminals.
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Whenmultiplespeakersaretobeconnectedto
theamplifier,thecombinedloadimpedanceforthe
speakersmustbecalculated.Theloadmustthenbe
connectedtotheappropriateamplifierimpedance
tap.Usethistabletoaidinselectingthecorrectim-
pedancematch:
STEREONORMALCONNECTIONS
Load
impedance
inohms
0.8to1.6
1.6to3.2
3.2to6.4
6.4andup
Connectfor:
1ohmoutput
2ohmoutput
4ohmoutput
8ohmoutput
Ifa loadimpedanceisusedthatislowerthanthe
outputimpedancetap,thenreducedpowerandpos-
sibledistortionwillresult.Ifa loadimpedanceisused
thatishigherthantheoutputimpedancetap,then
neitherthesignalnortheamplifierwillbeharmed
butthepoweravailableisreduced.
STEREOCONSTANTVOLTAGELINEOPERATION:
Whenspeakersaretobeusedinmanydifferent
rooms,ormanyspeakersareneededtocovera large
areawithsound,constantvoltagelineoperationcan
beused.Thisisconvenientforlargerhomeback-
groundmusicsystemsorforindustrialinstallations.
Appropriatelinematchingtransformersmustbeused
ateachspeakerlocation.The2 ohmoutputprovides
thestandard25voltconstantvoltagelineoutput.In
thestereomode250wattsisavailableforeach
channel.
STEREOCONSTANTVOLTAGELINECONNECTIONS
Foroutput
voltageof
25volts
Connectfor:
2ohms
MONOPHONICORSINGLECHANNELOPERATION
WhentheMC2250isusedasa monophonicor
singlechannelpoweramplifierthetwochannels
canbecombinedintwodifferentways.Bothwill
combinetoproduceupto500wattsbuttheavailable
impedancesaredifferent.MONOBRIDGE offersa
fewhigherimpedanceconnectionsthanMONO
PARALLEL.Eithermodecanbeusedfor2 or4 ohm
operation.Performanceisidentical.Monophonic
constantvoltagelineoperationcanalsobeused.
Theoutputsareconnectedasdescribedbelow.
WhenusingtheMONOBRIDGE mode,outputim-
pedancesof2,4,8,and16ohmsareaccomodated.
Outputconnectionsaremadebyconnectingtothe
outputterminalsaslistedbelow.Notethatneither
outputterminalisatgroundpotential.
MONOBRIDGECONNECTIONS
LoadImpedance
InOhms
2
4
8
16
Connect- Speaker
LeadTo:
Left1 OhmTerminal
Left2 OhmTerminal
Left4 OhmTerminal
Left8 OhmTerminal
Connect+ Speaker
LeadTo:
Right1 OhmTerminal
Right2 OhmTerminal
Right4 OhmTerminal
Right8 OhmTerminal
WhenusingtheMONOPARALLELmode,output
impedancesof½,1,2,and4 ohmsareac-
comodated.Connectaslistedbelow.Thecommon
outputterminalsareatgroundpotential.
MONOPARALLELCONNECTIONS
LoadImpedance
InOhms
½
1
2
Connect- Speaker
LeadTo:
EitherLeftorRight
CommonTerminal
EitherLeftorRight
CommonTerminal
EitherLeftorRight
CommonTerminal
EitherLeftorRight
CommonTerminal
Connect+ Speaker
LeadTo:
BothLeftandRight
1OhmTerminals
BothLeftandRight
2OhmTerminals
BothLeftandRight
4OhmTerminals
BothLeftandRight
8OhmTerminals
MONOPHONICCONSTANTVOLTAGELINE
OPERATION
WhentheMC2250isusedinMONOforconstant
voltagelineoperation,theMONOPARALLELcon-
nectionisused.Theappropriatelinematching
transformersmustbeusedateachspeakerlocation.
The1 ohmconnectionprovidesthestandard25volt
constantvoltagelineoutput.Inthismodea totalof
500wattsofmonophonicpowerisavailable.
MONOCONSTANTVOLTAGELINECONNECTIONS
Foroutput
voltageof
25volts
Connectedfor:
1ohmoutput(mono),monoparallel
BecertainthattheMC2250isneveroperatedin
thestereomodewiththeoutputsconnectedfor
monophonicoperation.ShouldtheMODESWITCH
beleftintheSTEREOpositionandtheoutputsre-
mainstrappedfora monoparallelload,onechannel
willattempttodrivetheotherwhichcauseshighcir-
culatingcurrentsandoverheating.
ACPOWER
TheMC2250operateson120volts50/60Hzand
requires12ampsatfullratedoutput.Plugthepower
cordintoa suitablesource.TheauxiliaryAC
OUTLETontheMC2250isnotfusedorswitched.
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Stereophonic
Connections
-6-

Mono-Bridge
Connections
-7-

Mono-Parallel
Connections
-8-